- It's hard to imagine the mountains around us exploding, sending molten rock into the sky and climate altering smoke high into the atmosphere, but it's definitely a thing, maybe even close to you.

There are over 160 potentially active volcanoes in the US and 1,500 worldwide.

On average, one of those volcanoes erupts every week.

And if you're wondering why we're talking about this on a show called Weathered, here's volcanologist, Alexa van Eaton, to explain.

- The most widespread hazard of volcanic eruptions is volcanic ash.

And so when that cloud buoyant plume of volcanic ash gets into the atmosphere, it becomes its own weather phenomenon.

And it can travel downwind hundreds to thousands of miles.

- [Maiya] These plumes can pose a serious threat to communities in their path, clogging streets, collapsing buildings, even suffocating humans and animals.

They can also be very sudden, shooting high into the atmosphere.

And the more remote and less studied the volcano the less likely there is to be an immediate or advanced warning.

- And that impacts aircraft.

- In fact, it can even cause them to crash.

Predicting eruption is not very accurate, so creating instant warning systems is crucial.

And one of those involves the lightning created by an eruption.

As recently as 2010, volcanic lightning was not well understood, but now it's becoming part of early warning systems all over the world.

Stay with us to learn how Alexa and her colleagues at USGS are using this beautiful and menacing weather phenomenon to make us safer.

(low dramatic thrum) We're in Vancouver, Washington where the United States Geological Survey has a volcano observatory, just miles for Mount St. Helens, which erupted in 1980 and may erupt again in our lifetimes.

(volcano bursting) It was the most destructive eruption in US history, killing 57 people and leveling hundreds of miles of forest and homes, and depositing 540 million to of ash downwind.

Less than 50 miles south is the Portland Airport, and 85 miles north, the Seattle-Tacoma Airport.

So that means a lot of air traffic.

And that ash is very different than what we're used to in the northwest.

- This is an example of volcanic ash from Mount St. Helens 1980.

As you can see, it's made out of tiny rock particles and these rock particles are a lot heavier and denser than wildfire ash, which is made out of burned biological material.

And you do not want to fly through this.

What happens is that the glass particles in ash melts in the jet engine and can cause flame out of the engine.

- [Maiya] And there's just too many volcanoes to monitor as closely as Mount St. Helens.

So on a cloudy day, for example, pilots may not know exactly where a plume could be.

- Frightening example of this happened in 1989, when a Boeing 747 jet was flying over Redoubt volcano, didn't realize it was erupting and flew directly into the ash cloud.

- [Woman] We have to go left now.

It's smoky in the cockpit at the moment, sir.

KLM 867, we have flame out all engines.

And we are descending now.

KLM 867 heavy, we are descending now.

We are in a fall.

(intriguing music) Luckily they ended up recovering their engines and landing safely, but that was a real wake up call to the airline community, to the volcanological community, that we need to have early warning and a coherent strategy for warning jet aircraft of when volcanoes are erupting.

- [Maiya] Every year, dozens of planes come in contact with volcanic ash.

And since 1980, the number of airline passengers has increased over five fold, meaning more flights over active volcanoes.

- So it's something you wanna avoid.

And to be able to avoid it you need scientists on the ground, monitoring the volcanoes, trying to figure out how high, how fast, how much ash is getting into the atmosphere.

- [Maiya] But sometimes, you can't get scientists on the ground, so you need a spider.

- This is the US geological survey spider, which is a temporary sensor package.

And the whole point of this is to be airlifted by sling load by a helicopter and dropped into a crater of a volcano or a place where we otherwise need data, but don't wanna send people because it's too unsafe.

And the first thing to land is the seismometer.

The point of this is to measure ground motion that might be associated with magma movement or rock fall, or eruptions inside the crater.

Okay, so I'm gonna go over to the data logger.

How about your crew come over here, make some ground motion for the seismometer, make some infrasound for the infrasound sensor, and make some sparks with the lightning detector.

And we can see what the data look like on the display.

- Okay.

Pick it up?

- Yeah.

- Okay.

(feet thumping) - [Alexa] Hey, we can see your jumps.

There they are.

Do two more.

- Okay.

(feet thumping) (Alexa giggles) - [Maiya] But it's not possible to get a station or spider on every volcano, and that's where lightning comes in.

- So volcanic lightning is a very new tool that we're starting to use for volcanic hazards.

Initially, it was something that took us by surprise that it happens during explosive eruptions.

Why do volcanic plumes become electrified?

You know, at first it was really a scientific question and something that was intriguing, but now it's becoming fundamentally useful.

- [Maiya] It piqued scientists' interest, because in the leading theory explaining meteorologic lightning, ice particles bump into each other, causing some parts of the cloud to become positively charged and other parts to become negatively charged.

Lightning happens when the charge equalizes, but volcanoes are hot.

So where does the charge come from?

Well, first, remember the ash.

- Volcanic ash is made of pulverized pieces of rock.

And so, if those ash particles are able to scrape together, they can create a static charge very close to the vent and start creating discharges of electricity.

Then, if the plume rises high enough into the cold upper atmosphere that the water carried inside the plume freezes, it forms ice, and the ice formation helps to trigger another phase of lightning activity.

Lightning produces a broad spectrum of electromagnetic energy.

Some of which is in the radio band and can be picked up by AM radio and specialized antennas.

So there's a global network of radio antennas that help us remove remotely sense large lightning from any eruption in the world.

And that can help us develop a general sense of which volcano's erupting around the world, how significant is it, and how high the ash cloud might be traveling.

- It's amazing how many people around the world live within range of being affected by a volcanic eruption.

So of course, we asked Alexa for some tips on how to stay safe and who should be focused on this kind of disaster.

- Now there are two major distinct hazards from volcanoes.

There's volcanic ash that travels downwind, and then there are the flow hazards, like lahars, which are volcanic mud flows.

And it can take out bridges and houses.

It's basically a muddy flood.

And that's not something that you wanna be in the path of.

The best way to be prepared for a volcanic eruption is to know your local hazards.

So, check the maps, know where you live with respect to the hazard zones for each volcano.

- Do you live in an area with volcanic activity?

How do you think about the risk?

Let us know in the comments and we'll see you next time on Weathered.

(light music)